Synthesis of polymethylene-linked bis(cyclobutane-fused chromanones) mediated by gold photocatalysis.

We report a gold-mediated energy transfer strategy for the sequential double [2 + 2] photocycloaddition of coumarins with dienes, providing access to polymethylene-linked bis(cyclobutane-fused chromanones). The reaction proceeds under mild conditions and affords structurally complex products in moderate to good yields. Optimization studies, control experiments, triplet-energy analysis, and DFT calculations support a triplet energy transfer pathway involving diradical intermediates.